Software release : The ETo calculator

The ETo calculator is a software developed by the Land and Water Division of FAO. Its main function is to calculate reference evapotranspiration (ETo) according to FAO standards.

ETo represents the evapotranspiration rate from a reference surface, not short of water. A large uniform grass field is considered worldwide as the reference surface. The reference crop completely covers the soil, is kept short, well watered and is actively growing under optimal agronomic conditions.

The ETo calculator assesses ETo from meteorological data by means of the FAO Penman-Monteith equation. This method has been selected by FAO as the reference because it closely approximates grass ETo at the location evaluated, is physically based, and explicitly incorporates both physiological and aerodynamic parameters.

ETo calculator version 3.1, issued in January 2009, is written in Borland DELPHI and runs in the DOS environment. The program is available in English, and is distributed as Land and Water Digital Media Series No 36. It includes a Reference Manual, which explains the use of the computer program.

The ETo Calculator is a public domain software, and an installation disk (1.5 Mb) and a software copy of the Reference Manual can be freely downloaded. If the ETo calculator software is correctly installed, it occupies less than 2 Mb on disk.

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• Go to the ETo Claculator Page 
• Go to FAO Water Database and Software Page